Many imaging applications such as Short Wave Infrared (SWIR) face challenges from thermal noise. In particular, low-light conditions require longer exposure times and higher gain that exacerbate the interference produced by thermal noise. It is thus conventional to cool image sensors in demanding applications to suppress thermal noise. Since there is no room in conventional cameras for vapor-compression refrigeration systems, image sensor cooling is typically performed using a solid state thermo-electric cooler (TEC). Although a TEC is compact and readily integrates with the circuit board holding the image sensor, thermo-electric cooling is quite inefficient as compared to traditional vapor-compression refrigeration techniques.
A conventional TEC-cooled camera sensor is controlled so that the thermo-electric cooler maintains a constant image sensor temperature such as 5° C. But the amount of power consumed by a thermo-electric cooler is proportional to the difference between the ambient air temperature and the desired image sensor temperature. For example, a TEC may consume 2 watts of power if the ambient temperature is 20° C. (requiring 15 degrees of cooling to bring the image sensor to the desired 5° C.). But operating conditions can be much hotter than 20° C. For example, a camera operating in a tank in the Iraqi desert may face ambient temperatures of 80° C. At such high temperatures, the TEC can consume 30 watts to cool the image sensor to 5° C. (a 75° C. difference).
Accordingly, there is a need in the art for more efficient image sensor cooling techniques.